One thing I'd like to point out is that even management gets this wrong sometimes. What your manager told you may not have been accurate. Having dealt with this from the HR side, it's entirely possible that, although you had "contact" with the individual, it did not meet the definition of "close contact" that would require specific actions such as your isolation.
For example, if you happen to walk past the individual who had been diagnosed several times a day, that doesn't mean you had "close contact". Or, if you had a 5-minute conversation with the individual, that doesn't meet the definition of "close contact".
Your company may, in fact, be following the requirements to the letter.