There are three reviews in ActiveCaptain for Lewis Bay East, which is marked as an anchorage. The latest review, however, was July 17, 2013.
Digging deeper, I found this in the Town of Yarmouth Harbor Regulations (Town of Yarmouth, MA HARBOR REGULATIONS
All vessels entering Town of Yarmouth waters are subject to the direction of the Harbormaster Department, which should be consulted before anchoring or tying up to any of the Town-owned facilities or moorings.
According to section 33 of the CFR;
§ 164.19 Requirements for vessels at anchor.
The master or person in charge of each vessel that is anchored shall ensure that:
(a) A proper anchor watch is maintained;
(b) Procedures are followed to detect a dragging anchor; and
(c) Whenever weather, tide, or current conditions are likely to cause the vessel's anchor to drag, action is taken to ensure the safety of the vessel, structures, and other vessels, such as being ready to veer chain, let go a second anchor, or get underway using the vessel's own propulsion or tug assistance.
[CGD 74-77, 42 FR 5956, Jan. 31, 1977]
In researching this, I came across a story of a transient captain in Scituate being told by the Harbormaster that he must rent a town mooring. The seasoned captain suggested the Harbormaster review his maritime law which apparetly allows for transient anchorage for up to 2 weeks, as long as you are out of the way of other boats. The Harbormaster apologized and let him stay.
I suspect that the Harbormaster was upset because he was not consulted before you dropped the hook, and would have raised a fuss over your not displaying the appropriate dayshape, or maintaining an anchor watch (which requires someone to be on the boat).
Also, In MA, where land owners own to MLLW, you have right of way on private property at low tide, if you are 'actively' engaged in fishing, which is why many people carry a pole when they walk the beach.