I have done a little bit of research.
1. How much clen is accumulated in beef muscle?
2. How rapid is the turnover (if you stop feeding the animal clen, how much is retained over time)
3. What is the clearance in the body?
Short answer, if it was a steak then it was absolutely riddled with clen, which makes no sense at all.
If you were givign clen to animals to boost lean weight you would typically stop 7-14 days before slaughter. Firstly because there is little benefit giving the drugs up to slaughter and secondly it gives them a chance to clear the system so they are not detected using standard methods. As soon as you stop giving clen the muscle concentration drops by 10-fold every day.
Clearance from the body - t1/2 is about 8 hours.
How much clen in a steak? About 15ng/g, so about 3.5 ug for an 8 oz steak.
Divide that by the volume of blood and you get 750pg/mL. Or about 15 times the detected amount. Now taking into account clearance rates, it must have been either a rather large steak, or the cow was drugged up until the day it was slaughtered. And there was a very efficient transfer of clen to the blood from oral ingestion. 75-90% passes straight through and is cleared via urine or faeces.
So either bertie was very, very unlucky or there was an exgenous source of clenbuterol, perhaps remaining after a regime from whence blood was stored for re-infusion later.