Unfortunately we don't have enough information here to know for sure. For example, the approach controller may have noticed that a plane they recently handed o

Unfortunately we don't have enough information here to know for sure. For example, the approach controller may have noticed that a plane they recently handed off to Tower was not yet lined up. The controller would then call up to Tower to make Tower aware of the issue. Or, Tower may have a screen showing them a radar view of the approach, similar to Approach's screen. They may have noticed it there. But, the nature of aviation radio is such that you use one frequency to transmit and receive. That means you can't speak over anyone else; you have to wait for them to stop talking before you can start. And if you mess up, there's no easy way for you to know (except when someone else on frequency says "blocked").