I believe they did this to not really be bound. They can retract the "pledge" unilaterally since there is no contract with anyone. Also, if you sue them for infringement you might find the pledge does not apply to you any longer.
If they wanted to, it is easy to file papers with the USPTO, etc. disclaiming a patent.
from the Tesla document -
A party is "
acting in good faith " for so long as such party and its related or affiliated companies have not:
asserted, helped others assert or had a financial stake in any assertion of (i) any patent or other intellectual property right against Tesla or (ii) any patent right against a third party for its use of technologies relating to electric vehicles or related equipment;
challenged, helped others challenge, or had a financial stake in any challenge to any Tesla patent; or
marketed or sold any knock-off product (e.g., a product created by imitating or copying the design or appearance of a Tesla product or which suggests an association with or endorsement by Tesla) or provided any material assistance to another party doing so.
They say "All Our Patent Are Belong To You" but - they will sue you under those patents if you were to challenge the validity of any of those patents. As the kids say "I call B.S."
Further, one of the things that the pledge says would let them break the pledge is if someone used their patents in bad faith. One of the examples of bad faith is "knocking us off". So, I can practice any Tesla patent including the design patent below, unless I'm knocking them off?