It's a possibility, but the protestors would have to have had a fast reaction time to the tip.
The cops in charge of her personal security would have had more advance notice of where she planned to be. If so, that is far more worrisome. A tip which results in protesters arriving could just as easily have turned into an assassination. The DHS secretary likely has been thinking the same thoughts.
As others are saying, I’m beginning to lean on the likelihood that the tipster was an Obama SwampDweller holdover at DHS.
And given the risks of assassination, I hope the Trump Administration looks very hard into this incident to find out exactly how it happened.