Normally a team would send a RB coach to meet with a RB. Seattle sent Bevell to meet with Ervin... that suggests to me that the Seahawks are pretty serious about the guy.
Williams, Collins and Dixon all ran a ~4.60 forty which likely eliminates them from consideration for Seattle. The 'slowest' RB Seattle has drafted was Christine Michael who ran a 4.54, but Michael also had an unbelievable 1.49 ten yard split at 220 pounds. Turbin ran fast. Lynch ran fast. (Rawls ran poorly, but was nursing a bad hamstring).
So if we assume Seattle is only looking at RB who are explosive burners, that shines a spotlight on a few guys (40 time, 10 yard split):
Keith Marshall: 4.31, 1.53
Tyler Ervin: 4.41, 1.56
Daniel Lasco: 4.46, 1.53
Marshaun Coprich: 4.47, 1.54
Wendell Smallwood: 4.47, 1.56
Josh Ferguson: 4.48, 1.56
CJ Prosise: 4.48, 1.57
DeAndre Washington: 4.49, 1.58
Those are the players who ran a sub 4.50 forty at the combine with a sub 1.60 ten yard split. Most of them are not serious NFL prospects. Of that list, Marshall, Ervin, and Coprich stand out the most. Lasco has awful tape, but his combine was so good that Seattle might go after him in UDFA.
Ervin is projected to go in rounds 4-5. Marshall is projected to go in rounds 5-6. Coprich is projected to go in round 7-UDFA. So not only do they fit Seattle's need for a super athletic RB, but they will likely be available around the time that Seattle would start to consider drafting a RB.
Of this group, Ervin has the highest draft projection, so it probably shouldn't be a shock that Seattle sent their OC to meet with Ervin at his pro-day.