Just showing a product at an exhibition is not considered distribution under any interpretation. That is as much distribution as showing a photo or video of the product.
For most licenses, including the GPL, there are two ways that distribution can take place (and he copyleft obligations start to apply):
- You physically hand over a device using the software
- You give someone outside your organisation control over the choice to install or remove the software
The AGPL license has another way that the copyleft obligations come into force and that is when users can use the software over a remote connection.
There is a chance that this clause triggers if you demonstrate software containing AGPL parts and allow users to play with it during the demonstration.
The copyleft obligation of providing source does not mean that you must actively hand out the source code, but rather that you must give it when people ask for it.