Not a stupid question at all. In fact, if that pilot was flying round buildings, he was probably breaking the law. Unless he was doing legitimate survey work with an on-board camera, say.
I assume from your YouTube comments that you are talking about internal combustion (IC) engines as opposed to electric motors.
I refer now to the IC engines, either 2 or 4-stroke types using methanol (glow fuel) with added lubrication already mixed in; either castor oil or synthetic or a mixture of both.
So the simple answer to your question is, yes.
The engines generally are constructed two ways. Those with a ringed piston and those that have a plain piston but the liner has a very fine taper at the top to increase the seal at TDC (Top dead centre) for the power stroke.
The terms RTF (Ready to fly) or ARTF (Almost ready to fly) usually refer to the aircraft being sold and indicates the varying amount of work needed to get it into flying condition, rather than the engine itself.
Having said that, the non-ringed engines can be flown carefully i.e. not flat-out, for the first four or five tankfuls of fuel at a slightly rich setting, so could be said to be RTF.
These engines are referred to as the ABC type. Aluminium piston, Brass liner which is Chromium plated on the inside.
The ringed engines need a bit more running-in. This can be done on the ground, in the plane, but is much easier on a test bench. The engine is started and the throttle opened to maximum but the needle is unscrewed so the engine is running very rich; almost 4-stroking is the phrase. This is done for five minutes and the engine is stopped and allowed to cool. You then repeat the procedure, screwing in the needle a click each time until you clocked about half-an-hours runnibg time. The larger engines will need twice that time. It's the alternate heating and cooling that helps the ring to bed-in with the cylinder liner.
If you're keen on giving R/C flying a try, check out the British Model Flying Association at www.bmfa.org and search for a club near you and arrange a visit. Resist the temptation to buy the first plane you see at a 'good' price and do not under any circumstances buy on-line until you have an informed idea of what you wish to fly.
I am a fixed-wing examiner for the BMFA so it's paramount that you understand the safety aspects of model flying. Go for it, but stay away from buildings! Buy a magazine, say the RCM&E or Model Flyer and take look at what's available. Good luck and happy landings.