That’s not right at all, but I can see that it’s a tricky spot, and your roof deck is boards instead of plywood… I dunno. If that was the only spot, i’d make them go in the attic and stick some wood in that gap. They can bridge from the other two boards and it won’t be great, but it won’t be horrible.
If there are more spots like this, i’d have another legit roofer who specializes in repairs (but ideally not full roofs) come out to inspect. Especially if the spots aren’t also obviously small, and difficult to actually add any real sopport. He’ll give you an unbiased opinion and tell you exactly what needs to be done to make sure you end up with a good roof, and likely give you an estimate in case you want him to do the work.
I know a good bit about roofing, and unless the roof was obviously done impeccably except for that, i’d be rather concerned. Sometimes it’s best to just leave something alone and not get into another several thousand dollars worth of repair, and I don’t know what that area of your roof looked like when he got down to the decking. A good roofer will. It’s time to get some outside advice. The municipality where you live also likely has roofing inspectors who have to close out any permits the roofer pulled. You can contact them and they’ll be glad to take a.look for free, but you might not get someone with as much knowledge as if you hire someone.