Forget your training and report it. You don’t want to be sued because your trainer/teacher was too scared to call it what it is. Below is the comment that I use. It lets them know about the fungi, states that it was not tested, could be a health hazard, informs them of the structural consequences if they let it remain and tells them what needs to be done now.
**Improve, Repair: **Signs of fungi growth is present on the wood structural components in the attic. A test to determine if this growth is or is not a health hazard is not included in this home inspection. The underlying cause is past or present moisture. Remediation will include removing the moisture source and verifying proper ventilation is available to the area as well as removing/killing the growth itself. If allowed to continue to grow this can, and most likely will, deteriorate the wood to a point that it will need replacement.