FZS600 engine oil warning light randomly comes on

[Fazerider]

I checked oil level and it seems it's fine, both when engine is cold and after a ride.
The light does seem to come on after fast accelerating. I thing it started when I changed the exhaust can few weeks ago and now I rev it high more often.
I haven't changed the oil for around 5000 miles now. Could it be a reason? I'm changing it this week

In that case, don't worry about it. The oil pickup is further back and will still provide the pump with oil despite the red light on the instrument cluster coming on under acceleration. 
When you change the oil, top it up to the upper mark after running the engine to fill the filter (assuming you're changing that too).