I'm sure you'd love to try to make that argument, but people who actually pay attention will note that Ovechkin is accomplishing what he does in entire seasons. He actually has 50 goal seasons, in a full 82 game season. That means, over a lengthy and difficult season that routinely sees players slow down, Ovechkin has proven he can maintain his pace enough to score 50 goals. And that's a feat that few NHL players accomplish, in large part because the 82 game season wears you down.
With Matthews, you can only take it in bits and pieces. Playing 82 games, in bits and pieces, and equaling 50 goals is not remotely the same as playing a full 82 game season, without the breaks, and equaling 50 goals. When the NHL starts awarding goal scoring trophies based on chunks of multiple seasons, then maybe you have an argument.
You might call Matthews a 50-goal scorer if he can put together 82 games where he scores 50 goals, regardless of them being 82 games in a row with breaks inbetween, but no one else will. Certainly no one who doesn't cheer for Toronto.
So, no. We won't find out this season. We may find out the next one, if Matthews can stay healthy enough to play enough games to have a shot at 50 goals. A ridiculously hot start this season would have gone a long way, but he was already slowing down before his injury, so who knows? On the other hand, we already know Ovechkin can do it. Repeatedly.