@Ric****
, okay, IF they did not get that extension based on marriage to a thai or based on visiting thai family here they were stamped by mistake and they WILL be on overstay AND fined for it if they foolishly think they can stay for 60 days on a 30 day extension to a 30 day visa exempt entry stamp.
It is the passport holder's responsibility to make sure they are stamped in for the correct amount of time.