Since there's little technical detail it's hard to be certain, but I doubt this is useful as a proof in the way one might wish (that is, proving that a web server delivered content X at date Y). The reason is, it does not appear that anything prevents the user from modifying the web page and then generating a "proof" about the modified version.
TLSNotary (tlsnotary.org) is an example of a project that attempts to use a (modified) TLS connection for non-repudiation (which is roughly the property that we would want here), but it requires a trusted third party to act as the notary.
It's possible this project is taking a similar approach (which would be fine, for those who trust the trusted third party). But given the lack of technical detail, and reading between the lines, I don't see a reason to believe this is the case.
(Happy to be wrong, though! Maybe a more detailed description would help us understand what's going on.)
TLSNotary (tlsnotary.org) is an example of a project that attempts to use a (modified) TLS connection for non-repudiation (which is roughly the property that we would want here), but it requires a trusted third party to act as the notary.
It's possible this project is taking a similar approach (which would be fine, for those who trust the trusted third party). But given the lack of technical detail, and reading between the lines, I don't see a reason to believe this is the case.
(Happy to be wrong, though! Maybe a more detailed description would help us understand what's going on.)