"because they may permit the growth of Clostridium botulinum". While the title state the 'presence' of Clostridium botulinum, the text states that the 'product presents the opportunity for growth'.
The CFIA statement does not go into any detail on the issue. In terms of risk, the mere presence is not an issue. Clostridium botulinum spores may be present in this natural product, but the concern would be growth of the organism, during which, toxin can be formed. C. botulinum requires an anaerobic environment for growth, that is, an environment that has low oxygen levels. To prevent this in mushrooms, the containers are perforated to allow air to exchange into the container. So while not exactly stated, one would guess that the mushrooms were packaged in plastic overwrap without that plastic being perforated (no holes).
Food Recall Warning - Belle Grove brand Whole White Mushrooms recalled due to potential presence of dangerous bacteria
From: Canadian Food Inspection Agency
Recall date: January 9, 2021
Reason for recall: Microbiological - Clostridium botulinum
Hazard classification: Class 1
Company / Firm: Monaghan Mushrooms Ltd.
Distribution: Ontario
Extent of the distribution: Consumer
Reference number: 14169
Food Recall Warning - Belle Grove brand Whole White Mushrooms recalled due to potential presence of dangerous bacteria
From: Canadian Food Inspection Agency
Recall date: January 9, 2021
Reason for recall: Microbiological - Clostridium botulinum
Hazard classification: Class 1
Company / Firm: Monaghan Mushrooms Ltd.
Distribution: Ontario
Extent of the distribution: Consumer
Reference number: 14169