Great question. For me, I don't find anything wrong about someone wanting a serious relationship on a dating app. Here are the reasons why:
1. Honesty. The person is just honest about what he wants and he is clear about his goal. I think that being genuine is very important so he can filter those only that are also interested with long term relationship and not those seeking for short time ones. What if you already are having fun spending time and talking to someone but later on you discovered that that person is not interested on having a long term relationship just like you do, then it would totally not work out right? It is better to tell what you want from the start to be clear and not beat around the bush.
2. There is nothing wrong with seeking long term relationships in dating apps. I think that being in a relationship sometimes is being romanticized. For example, first time meetings. Just because you met on a dating site does not mean your relationship means less than others. Yes, swiping left or right is easy but being able to meet that person and finding out if you two really clicked is kind of difficult too. Dating sites are often misunderstood. But I think, with proper and responsible usage, there is a possibility of landing on to a great relationship.
Personal or digital. Wherever you first met, I think it does not matter that much. What matters the most is that both of you really are willing to commit and work with your relationship together. Whatever makes you happy,as long as you are not hurting other people then go for it. I hope I was able to answer your question.