How does biblatex decides on the number of authors in a citation

Question

When I compile the example below I get Hailey et al. 2018 in the pdf. When I uncomment the second citation I get "Hailey, Mori, et al. (2018)Hailey and Mori (2017)." Why did the first reference change when I un-commented the second one ? I don't want this behavior.

I understand biblatex sometimes adds authors to disambiguate citations but that seems unneccessary in this case...

\documentclass{article}
\usepackage{filecontents}
\begin{filecontents}{mwe.bib}
@InProceedings{hailey&mori2017,
  Title                    = {{NuSTAR observations of black hole binary candidates in
 the Galactic Center and its environs}},
  Author                   = {Hailey, C.~J. and Mori, K.},
  Booktitle                = {AAS/High Energy Astrophysics Division},
  Year                     = {2017},
  Month                    = aug,
  Pages                    = {109.12},
  Series                   = {AAS/High Energy Astrophysics Division},
  Volume                   = {16},

  Adsnote                  = {Provided by the SAO/NASA Astrophysics Data System},
  Adsurl                   = {http://adsabs.harvard.edu/abs/2017HEAD...1610912H},
  Eid                      = {109.12},
  Owner                    = {aleksey},
  Timestamp                = {2017.10.13}
}

@Article{hailey+2018,
  Title                    = {A density cusp of quiescent X-ray binaries in the central
 parsec of the Galaxy},
  Author                   = {Hailey, C.~J. and Mori, K. and Bauer, F.~E. and Berkowitz, M.~E. and Hong, J. and Hord, B.~J.},
  Journal                  = {Nature},
  Year                     = {2018},

  Month                    = apr,
  Pages                    = {70--},
  Volume                   = {556},

  Owner                    = {aleksey},
  Publisher                = {Macmillan Publishers Limited, part of Springer Nature. All
 rights reserved.},
  Timestamp                = {2018.04.07},
  Url                      = {http://dx.doi.org/10.1038/nature25029}
}
\end{filecontents}

\usepackage[backend=biber, natbib=true, minnames=1, maxnames=2, style=authoryear]{biblatex}
\addbibresource{mwe.bib}


\begin{document}
\citet{hailey+2018}%\citet{hailey&mori2017}
\end{document}