Their use of the data is subject to section 4.3 of the ODBL. The language there demands a notice "reasonably calculated" to make the user "aware" of the data source. It doesn't demand on map attribution.

Attribution on the map is a clear, easy way to meet that bar (and acknowledges the many OSM contributors that see a prominent notice as being necessary to meet the license), but it isn't clear that the court tested bar will be so high.

Note that I'm not drawing "We'll see you in court" as a good way for a company to act towards a community, just commenting on where and how their obligations are defined.