Um... yes, that is excessive. I think they need to be far more diligent. Two is not too young or old for a child to be given a 'safe space' to play if the parent cannot shadow the child.
See, it sounds to me like this:
Things get busy,
Mom and dad are distracted,
Kiddo wants attention
BITE!
Kiddo gets attention, albeit negative.
When I worked with an older toddler group, for 2.5 years, we did have some kids who bit. When those children were becoming 'repeat offenders', we had a teacher shadow that kid, sit close to them, able to watch them and move quickly when we saw them go for the bite (it's usually quick but obvious) and interrupt it, then offer them a teething toy. "No biting so-and-so, you can bite on this".When I was a nanny, if I couldn't be close to a child who was biting, they often went into the pack and play or a high chair or other containment device. "You may not bite" or "you need to sit here now". Calm, firm, ignore them while I helped the hurt child. "No bite, you sit here now."
If I were in your shoes, I'd take a break on getting the kids together. If your friend asks, just tell her the truth-- Charlie bit my kids several times when we last visited and they aren't ready to go back.