It's whether it's a possibility worth worrying about. IMO it isn't because it's just so remote.
I don't see the similarity to 2005, except that they're clearly not the best team in the competition. We were massively unlikely to win that, but some signs were there.
For a start, we absolutely hammered Leverkusen in the last 16, a better side than Utd just beat. We were clearly gaining momentum at that point. Utd just barely scraped through against one of the worst teams in the competition.
We had an exciting new manager who was taking his time adapting to the PL but who everyone was behind. A manager who'd achieved great things in the recent past, including winning in Europe, and had just taken us to a League Cup final. Utd have David Moyes, their equivalent to Roy Hodgson, who about 95% of their fans want sacked. It's a completely different situation, psychologically.
Also, as others have said, that team did, on its day, have one outstanding quality: its defence. That meant it could go to Juve, it could go to Stamford Bridge, and just soak up pressure. It had some kind of strategy for beating better teams.
Sorry, but they've got about as much chance of winning the CL as they have of catching us in the league. That's *possible*, but it's hardly worth worrying about, is it?