With air hardening steels there's only a certain range of heat that will soften it. If the builder went too far and tried to anneal the steel, he will have hardened it. If the builder went too little, he basically did nothing except damage the paint. If he got it just right, then it's still not as ductile as 653. Heat treatment generally isn't in the realm of a frame builder's toolset, and truisms for say heat-treated 4130 don't apply to 853, so I don't know what your framebuilder did or did not do.

The state of temper is more or less based on the maximum temperature the steel was brought up to post-quench. Generally speaking, as temperature goes up, strength decreases and ductility increases. For example a 600C temper will usually be harder and less ductile than a 700C temper. Heating it again afterwards to 500C isn't going to help. Now there's also stress relieving, where you bring up the temperature fairly high and hold it for a while then let it cool, but I don't know the correct procedure for 631/853. Reynolds intends for 631/853 to not require it for normal construction. In most cases, tempering the steel excessively would generally be considered damage to the heat treatment since it lowers strength. Again, there's an upper limit to tempering, once you hit critical temp (which brass/welding will), it's no longer tempering and will either harden when quenched (air for air-hardening, oil bath for 4130) or anneal (really more like normalize) when cooled slowly (hours of dropping temps in a furnace for air-hardening, air for 4130).

So the answer is maybe your frame builder tempered the steel and made it more ductile. Maybe he didn't. Maybe it could be tempered more.