We can basically take it as two ways, either the opening cutscene is canon, or it's not. If it is, then ground combat did occur, because of several reasons.
1. All of those are combat troops. To be massed in such away indicates they were organized. If they were "debris" from a destroyer, they bodies would be scattered, you'd see mostly scattered body parts, not intact humans, not to mention you'd expect to see other debris interlaced between, and indeed, in them, which you don't see.
2. If they were killed by Lucy beams, they'd be vaporized.
3. If they were at the edge of the radius of an attack evacuating civilians, where are all the civilians.
Conclusion: Logically speaking, if the cutscenes is indeed canon, then ground combat did, in fact, occur. There is no other logical explanation for what we see in the cutscene. However, it is possible that the cutscene is not canon, thus ground combat did not occur.