IMO, winning and making profit in sports betting is more of skill-based rather than luck. Though there is always an element of luck when you try to place a bet in any form of gambling. However, sports betting requires knowledge, know-how, familiarity of which sports you laid your interest in, and of course the odd & match-up analysis, which plays a vital role in determining your chances of winning.
When someone is placing bets mindlessly and were able to come up winning, then that's what you call a pure luck. I don't believe a lot of sports bettors are actually doing it. Because most of us would analyze the odd vs the match-up before placing bets.