Nursery concerned about DS "in his own world"

[NotNob]

Hi
We are awaiting a GP referral. DS's nursery have suggested he be referred but are unwilling or unable to say what their suspicions are. He is 3 years old and has been described as "in his own world" and is happy to play on his own rather than with other children. They are encouraging him to play with others but even when appearing to do so, is still just playing his own games. He's quite obsessive about certain games - ninjas and other such, picked up from his older DB - and insists only only playing these games.
He also had some vacant moments when he will sit alone at nursery, sometimes staring apparently into space, until a teacher speaks to him. They have mentioned absense seizures but I have yet to witness anything. He does seem to have a vivid imagination, and as he walks along, at school pick up for example, he will jump, run, fight, pretending to be a ninja. I can see what they mean about his own world but I put this down to a good, somewhat intense imagination.
He socialises well with his DB but they do share playing interests. He also plays well with his cousin of a similar age.
Other observations: his speech is very good, motor skills fine, empathy great, eye contact good and excellent at numbers, alphabet etc. He loves the colour yellow, grinds his teeth (daytime) incessantly and is very strong willed. He jumps a lot when excited. He is stubborn and very active. Sensory issues are mild; mild dislike of loud noises and doesn't like eating or drinking anything which is too warm or too cold. Time out doesn't not work. He does not seem interested, particularly in other children but only in playing his own games.
A recent audiology report has come back as mild hearing impairment in one ear through glue ear. Review in a few months.
DH is convinced there's nothing wrong with him, along with my DSis who knows him well. I am an anxious person (health anxiety) but even I wasn't concerned or had noticed anything until nursery spoke with me. They say he is an enigma, there are some red flag, when I've asked his key worker about ASD, she says she's not convinced but wonders if it is more than developmental. GP doesn't seem overly concerned but stated as we're not experts and nursery have flagged it, we should refer to comm paeds, SALT etc.
Anyone relate to this? I am anxious yet also slightly defensive about him as he's still young. I'm hoping he's just quirky.
Any thoughts or advice much appreciated. Sorry it's long and rambling

[NotNob]

Hi. Thanks for responding. The red flags are not socialising as they would expect, problems following instruction eg washing his hands, putting on shoes. I have noticed this too; he's capable but doesn't want to. His vacant moments when he sits alone, seemingly in his own world. Sometimes he tantrums at nursery when he's asked to do something he doesn't want to.
He is the opposite of independent, but perhaps just v lazy.
Eating is good, has his likes and dislikes but generally easy.
Sleep is rubbish, fine going to sleep but comes in with us in the middle of night.
He's fine with routine change.
When he's bored he complains?
He hates being told something he doesn't want to hear - currently tantruming cos he can't join in Xbox game with DB and his friend!

[NotNob]

Thank you polyergoose, the audiologist did say in a nursery environment he could be affected.

zzzzz I think so, but I see him only with children he knows well. Perhaps of significance is his older brother was under brief investigation while at a different nursery for social skills. Someone from the council development team (I think) was brought in to observe him as he didn't like being around other children. They concluded he was fine but there were no other "red flag" aside from this. It took him until year 1 at school to make "proper" friends and they remain a small select few. He still can be a little socially awkward but he's fine and school have no concerns as far as I know. Perhaps DC2 is similar, but much less introverted than DC 1.

[NotNob]

zzzzz playgroups/swimming/events all great, loves them.

[NotNob]

I should probably also mention he is not socially shy at all, just doesn't seem to get it, for example, when he meets another small boy he will go to play fight them, assuming they are in the know regarding his ninja game.

[NotNob]

Thank you zzzzz