I don't think you should read too much into that... last year on here some people got it straight away and others didn't. I was one that did (like this time round) and I was still a ballot reject lol
I've always been led to believe that it's fine to cross-train in that way. It's pretty rare I have a full day off. On my run rest days I weight train or do aerobics, pilates etc
I think it's just important to listen closely to your body and if you are fatigued be prepared to take an unscheduled day off all exercise to give your body a little respite.