If it's any consolation, which i may not be by the time you've finished reading this, my son was equally loving towards me at that age. Not only did he not even say "mummy" until near enough 21 months, having gone from three words at 20 months (cat, lorry and daddy) to complete sentences a month later, but when he started actively chatting, his sentiments were less than loving. I fondly remember the times he said to me (aged less than 2.3) "Mummy, I want you to die so that Daddy can look after me", followed by such an obsession with knives that I had a friend ask a child psychologist for me because I was too chicken. Was seriously worried about my child being a psychopathic matricidal maniac...
Anyway, to cut a long story short, he is now nearly 14, is absolutely lovely, articulate, and loving (although not big on hugs or kisses) and he never did murder me.
Even when Benedict said those things to me, I knew he didn't mean them, and somehow managed not to take them personally. He just couldn't articulate what he really meant- that he really really did not want his little sister.
I think it may a phase some of them go through... He loves you though, have no doubt about that.