Glitch or cheating?

So I was in a 3v3 game and I was going against a , , and . It started of normal until I noticed (5:00 mins in the game) that I couldn't find or on the map. I asked my team if they saw them and they said no. I then asked the other team and they said yes. I continued on and the I was going against took no damage from me or my teammates. I starting thinking they were hacking. The invisible then took down the tower and instead of showing (player) took down a tower, it showed a purple box and and some words with _'s. I was playing and said "You are getting ddosed Cait" Was this really hacking or was the game just being glitched?