M.D.
I think it's very common for babies to focus on the new skill and "forget" the old skill while mastering the new one. Our son went through a phase where he really didn't talk/coo/babble - right about the same age your son is. He was really working on crawling at that point. DS also didn't fully belly laugh until he was 8ish months old either. It was really hard to even get a chuckle out of him before that. He was very social though and making eye contact etc. FWIW, he didn't raise his arms to be picked up until he was close to a year. He was just such an independent baby! There's also something called Word Mortality - though more common with older babies I think, maybe it could explain your DS's behavior. Babies will often learn a new word or sound, use it for a week and then "lose" it. DS still does this. It's perfectly normal (according to an SLP I know).
Anyway - DS is completely on target verbally and socially these days as well as physically. He talks (some real words & a LOT of his own language), signs, and shows emotions. He hugs, kisses, and asks to be picked up, though he did start these things later than some, he's more than made up for it these days. I'm confident that right now he's not on the Autism Spectrum.
BUT - what I've said is in NTBCAMA. And if you are worried, do talk to your pediatrician about it.