4 year old- is this shyness?

[Tiredmummy224]

I'm not really sure if shy is what I'd describe him us but wonder if it's some version of it ?
His teacher asked about referring him to speech therapy, because he just doesn't talk at school.
He talks non stop at home
In fact he never stops talking at home
He had a school play, he didn't even sing along with the songs
After the play when I went to speak to him all I got were nods of the head
No verbal responses to anything at all

When someone says hello to him he'll smile and way but won't respond

Even with friends at school
He'll tell me about his best friedns and will run to them in the morning but never seen him actually speak to any

If we take him to play centre or playground he doesn't seem to have issues approaching other children to play with them but again he won't utter a single word to them

Is this some kind of version of shyness or something else?
Besides that he's always happy bright boy it's just talking to anyone

He's shy. My 2nd son was like that. He used to chat all the time at home, with us. I was called into the nursery one day (he went 1/2 days) because they said he couldn't speak - they'd never heard him). He continued to be like that until he was 6 or 7, wouldn't talk to teachers or other kids, only gave yes/no replies, didn't engage with anyone except family. He went on to be very academic, intelligent, thoughtful and confident. He's almost 40 now, has a good job (leads a team), a family, etc., and is very outgoing.

@HandyLittleGadget thank you for your comment
It helped to read how your one developed and managed to get over it until he got older