i think it unlikely that he took steroids, but there are plenty of athletes reaping the benefit of increased base strength and faster recovery time that many anabolic steroids give without increased mass.
They are abused in everything from Bodybuilding to Badminton at international level.
it takes a long time for steroids, especially those available 30-40 years ago, to be fully flushed from the body. Athletes go to great trouble to ensure they have 'clearance time' prior to competition, this way the blood looks 'clean' if tested.
Recreational users do not have such worries, and often do not cycle steroid use in such a way that they leave the system completely, leaving trace deposits in some major organs, including the liver.
there was no trace of such substances found in Bruce Lee's post mortem, and seeing as how he had no reason to mask the presence of steroids in his system, it is unlikely that they would not presesnt themselves by some quirk of fate.