In a word, Yes.

Each itinerary you buy buy is a contract for the airline to give you transportation from A to B. In your case, you booked a ticket, and UA was required to get you to MUC, while you had a separate contract with OS to get you from MUC to wherever your end destination was. To save on price, many people do this. But in your case, it didn't really save you.

If you do this, it realistically requires a multiple hour stop to protect you from issues like this. For example, if your OS flight was booked to leave 5 or 6 hours later, a 2 hour delay wouldn't have made a difference. As you found out the hard way, separate tickets don't offer you protection. Even longer connections can backfire (I.e, flight cancelation and no way to get you to first destination for 24 hours), however, he longer between, the less risk.

On another note, if you had booked on 1 itinerary, you would have been rebooked by UA to your final destination.

Sorry you learned this the hard way.