You experienced what is called a "sensor ghost", it's basically a glitch in your fleet sensors, though in-game they actually have some interesting properties.
The following will be mild spoilers on that particular mechanic.
Some of those will interdict pulse your ship, cancelling your sustained burn, you must use your own interdict pulse on them so they disappear, some will come towards you and then fly slowly away, if you follow them they'll lead you to salvage or a fleet of enemies.
Lastly the coolest one, is a sort of cloud of signal that just sits there in hyperspace, if you interdict pulse on it, it'll start creating a slipstream in the opposite direction of your fleet, so you can create a passage by putting the sensor ghost between you and your destination.
Most are simply harmless, serve no function, and are there to freak you out a little bit.