In mid-May Lee was telling Jackson to attack Banks as quickly as possible and drive him out Valley while Johnston cautioned him that if Banks was heavilly invested it would be too hazardous to attack him, and on May 17 Johnston wrote to Ewell telling him that if Banks's position was too strongly fortified they should leave him where he was and strike out at Sheilds as he was marching to Fredericksburg instead, this message was forwarded to Jackson.
On May 18th Johnston sent two letter to the Valley. In one to Jackson he reiterated that the goal was to keep Banks from linking up with McDowell and if he was too late to achieve success by attacking Banks directly he should look to east outside of the Valley for a better opportunity, he also stated his full confidence in Jackson and Ewell's judgement and left the final decision of what to do up to them. In the second to Ewell he wrote :
"The whole question is, whether or not General Jackson and yourself are too late to attack Banks. If so the march eastward should be made. If not (supposing your strenght sufficent) then attack."
Page 164 - Joseph E. Johnston and the Defense of Richmond - Steven Newton
Jackson's communication to Lee on May 20th in light of that, therefore, seems less like a plea to keep Ewell in the Valley and countermand an order from Johnston for him leave it than it does as merely a request for confirmation of what freedom he has and whether he is allowed to attack Banks or not.