Units for "Total Memory", "Avg Memory" and "Max Memory" columns are not the same in SAP HANA | SQL PLAN dashboard. "Avg Memory" column is measured in "MB" where as the other two columns are measured in "GB".
This is by product design.
Total memory should be executions x avg memory, so these metrics can be expected to be on a different scale for the most active plans.
Memory metrics are available at the byte scale from HANA. If a plan uses only bytes or KB of memory, it's likely it won't be a major target of monitoring, whereas scaling everything to GB could potentially obscure all but the very largest plans.