Typical DN42 interconnects are 1Gbps with unspecified bandwidth caps. It's not made to carry serious traffic at all. For a real ISP, 5000 Mbps these days is nothing unless it's all concentrated on the same last mile - the smallest links they use are usually now 10Gbps. But DN42 isn't the real internet.
I think the owner wanted 100 Gbps of scan traffic or had set a specific scan-rate target, which determined that bit rate, so the LLM (correctly) predicted it needed all of those to hit the target.
100Gbps? I don't think so? I'd expect a thousand a month for the adapter and connection, and then around $1.50/TB as per their standard price (including currency conversion and VAT), which is to say, $1.00 per minute of saturated usage.