I don't think it would be connected since they say that straw cups are better for kids to learn how to chew, swallow, speak etc and thumb sucking would have the same affect as a straw cup lol.

I would let mom know that I am discouraging the thumb sucking as much as possible at daycare. I think the rest will come in time. Children develop at different ages so try not to compare him to the others too much just quite yet