I saw it by my own eyes when I was child. Old wooden fence started to burn after cigarette butt landed at it in hot summer. Wood was dry and hot in direct light. I saw little smoke first then smoke disappeared, then, after couple of minutes, clean fire.

You saw the combustion equivalent of being bit by a shark and struck by lightening at the same time. Except in exceptional circumstances where the wood is highly flammable (like very dry and probably a little bit rotted wood that's at 150F+ from sitting in the sun), something like a cigarette butt or a lit match is not enough to catch lumber on fire without some other easier to ignite material in between as a stepping stone.

You seem to be quite mistaken: https://www.fire.nsw.gov.au/page.php?id=327

Your link deals with cigarette butts igniting brush on the roadside and hay in a lab simulating roadside conditions, not lumber. Nobody here is claiming that cigarette butts can't light dry brush on fire. I am claiming that in less than "freak accident" or laboratory conditions it is basically impossible to ignite lumber with a cigarette butt unless there is something (like dry brush) in between.

Edit: Based on the down votes I'm illiterate, I'm wrong or this is Reddit.

Current cigarettes have additives in the paper so that they go out easily themselves.