Not necessarily. It's well possible that United wanted to loan him out no matter what and in the end had to accept that they couldn't force him to a club of their liking. The reason why I think so is how things developed over the summer:
IIRC, first rumors that United wanted to send Januzaj on loan appeared some time in July or early August. They came from different sources, not just quoted or recycled ones, and included a number of different clubs from different leagues. I'm therefore inclined to believe that United had the firm intention to loan him out but not to sell him. I also recall some statements (from Belgian media? Don't know exactly, sorry.) that Januzaj refused interested EPL clubs. United cannot force Januzaj to a club he doesn't want to be loaned to.
IIRC, the first rumor in Gemany appeared on Sky Germany, saying United wants to loan him out but Dortmund would not be interested without some sort of buying option. Juventus was mentioned as an alternative. This was about 2 weeks before deadline day.
Then, things went quiet RE: Januzaj and Dortmund, and we were linked to Yarmolenko (vaguely confirmed by Thomas Tuchel). When this transfer didn't come to fruition, all of a sudden the loan of Januzaj was announced.
I can understand what you're saying but wouldn't agree. Sphaero explained it much better than I could do it in his post above where he addressed the "Rooney, Martial, Mata would be 1st teamers at Dortmund".